Cooling unit

ABSTRACT

A cooling unit which contains refrigerant for exchanging heat with an object member of cooling includes a refrigerant passage and cooling means. The refrigerant passage allows the refrigerant to circulate therethrough. The cooling means communicates with the refrigerant passage for supplying the refrigerant passage with the refrigerant. The cooling means includes a refrigeration circuit, a compressor, a condenser, decompression means, an evaporator, a refrigerant supply path, a refrigerant return path, refrigerant control means and first pressure control means. The refrigerant control means has an on mode which allows the refrigerant to circulate through the refrigerant passage at a flow rate which enables the refrigerant to maintain gas-liquid two-phase flow by allowing the condenser to communicate with the refrigerant passage, and an off mode which prevents the refrigerant from circulating through the refrigerant passage by preventing the condenser from communicating with the refrigerant passage.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling unit, and in particular to a cooling unit which requires strict temperature control for use in a semiconductor production unit.

In a conventional cooling unit such as a chiller unit for use in a semiconductor production unit, primary refrigerant such as fluorocarbon which circulates through a refrigeration circuit cools secondary refrigerant such as water, and the cooled secondary refrigerant cools an object member of cooling. In this case, the object member is not directly cooled by the refrigeration circuit but is indirectly cooled by the refrigeration circuit through the secondary refrigerant thereby to degrade cooling efficiency of the chiller unit.

To solve the above problem, a chiller unit in which an object member of cooling is directly cooled by only refrigerant such as fluorocarbon which circulates through a refrigeration circuit is disclosed by Japanese Unexamined Patent Application Publication (KOKAI) No. 2003-174016. In this chiller unit, the refrigerant compressed by a compressor of the refrigeration circuit is condensed by a condenser of the refrigeration circuit, and then the condensed refrigerant is transmitted into a refrigerant passage formed in a susceptor of a vacuum treatment unit through a regulating valve which regulates flow rate of the refrigerant thereby to cool a body to be treated which is disposed on the susceptor. That is, the refrigerant passage itself serves as what is called an evaporator of the refrigeration circuit. The refrigerant which has cooled the body is returned to the compressor so as to circulate through the refrigeration circuit again.

However, when the chiller unit of the above reference is applied to a case where an object member of cooling which is expected to reach temperature above a boiling point of the refrigerant is maintained at a constant temperature above the boiling point of the refrigerant, the conventional cooling method in which the regulating valve of the chiller unit controls the flow rate of the refrigerant cannot maintain the object member at the constant temperature due to the temperature of the object member above the boiling point of the refrigerant. That is, even if a part of the object member is maintained at the constant temperature, the other part of the object member is not maintained at the constant temperature. Consequently, temperature in the object member becomes irregular. Specifically, when the flow rate of the refrigerant flowing in the refrigerant passage is extremely small, even if the refrigerant is capable of cooling the object member in the vicinity of an inlet of the refrigerant passage, the refrigerant is completely vaporized or dried out in the middle of the refrigerant passage, so that absorption of heat using latent heat of vaporization is not performed. In this case, temperature of a part of the object member adjacent to an outlet of the refrigerant passage rises above that adjacent to the inlet of the refrigerant passage. That is, temperature in the object member becomes irregular. On the other hand, when the flow rate of the refrigerant flowing in the refrigerant passage is excessively large, a part of the object member adjacent to the inlet of the refrigerant passage is overcooled, so that temperature control is lost and therefore the object member is not maintained at a predetermined temperature.

SUMMARY OF THE INVENTION

The present invention is directed to a cooling unit capable of substantially uniformly cooling an object member of cooling to a desired temperature.

In accordance with an aspect of the present invention, a cooling unit which contains refrigerant for exchanging heat with an object member of cooling includes a refrigerant passage and cooling means. The refrigerant passage allows the refrigerant to circulate therethrough. The cooling means communicates with the refrigerant passage for supplying the refrigerant passage with the refrigerant. The cooling means includes a refrigeration circuit, a compressor, a condenser, decompression means, an evaporator, a refrigerant supply path, a refrigerant return path, refrigerant control means and first pressure control means. The refrigeration circuit allows the refrigerant to circulate therethrough. The compressor is disposed in the refrigeration circuit. The condenser is also disposed in the refrigeration circuit. The decompression means is also disposed in the refrigeration circuit. The evaporator is also disposed in the refrigeration circuit. One end of the refrigerant supply path is connected to a part of the refrigeration circuit between the condenser and the decompression means and the other end thereof is connected to an inlet of the refrigerant passage. One end of the refrigerant return path is connected to an outlet of the refrigerant passage and the other end thereof is located downstream from the decompression means and is connected to a part of the refrigeration circuit between the decompression means and the compressor. The refrigerant control means is disposed in the refrigerant supply path for allowing the condenser to communicate with the refrigerant passage or preventing the condenser from communicating with the refrigerant passage. The first pressure control means is also disposed in the refrigerant supply path for controlling pressure in the refrigerant passage. The refrigerant control means has an on mode which allows the refrigerant to circulate through the refrigerant passage at a flow rate which enables the refrigerant to maintain gas-liquid two-phase flow by allowing the condenser to communicate with the refrigerant passage, and an off mode which prevents the refrigerant from circulating through the refrigerant passage by preventing the condenser from communicating with the refrigerant passage.

It is not intended that the invention be summarized here in its entirety. Rather, other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description, together with the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing a cooling unit according to a first embodiment of the present invention;

FIG. 2 is a graph explaining an on-off control of the cooling unit according to the first embodiment of the present invention;

FIG. 3 is a graph representing the relationship between flow rate of fluorocarbon R134 which circulates through a refrigerant passage 3 and temperature fluctuation which is temperature difference between maximum temperature and minimum temperature in a shower plate 2 of the cooling unit according to the first embodiment of the present invention;

FIG. 4 is a schematic diagram showing a cooling unit according to a second embodiment of the present invention;

FIG. 5 is a schematic diagram showing a cooling unit according to a third embodiment of the present invention;

FIG. 6 is a schematic diagram showing a cooling unit according to a fourth embodiment of the present invention; and

FIG. 7 is a graph explaining the relationship between a duty ratio and circulation of fluorocarbon in a cooling unit according to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of the present invention with reference to the accompanying drawings.

A cooling unit according to a first embodiment of the present invention will now be described with reference to FIG. 1. In the first embodiment, a chiller unit 10 that serves as cooling means and a refrigerant passage 3 form the cooling unit.

A vacuum treatment unit 1 includes a vacuum chamber 6 therein. In the vacuum chamber 6, a susceptor 4 on which a body 5 to be treated is disposed is provided. In the upper part of the vacuum chamber 6, a shower plate 2 that serves as an object member of cooling is provided so as to face the susceptor 4. Inside an upper wall 7 of the vacuum treatment unit 1 in the vicinity of the shower plate 2, a refrigerant passage 3 is provided. Also, inside the upper wall 7, a temperature sensor 8 that serves as temperature detection means is provided for detecting temperature of the upper wall 7 in the vicinity of the shower plate 2.

The chiller unit 10 includes a diaphragm type compressor 11, a condenser 12, an expansion valve 14 that serves as decompression means, an evaporator 15 and a refrigeration circuit 18 through which fluorocarbon R134 a (hereinafter referred to as fluorocarbon) that serves as a refrigerant circulates. The compressor 11, the condenser 12, the expansion valve 14 and the evaporator 15 are disposed in the refrigeration circuit 18. The refrigeration circuit 18 includes a cooling-water path 16 through which cooling water circulates. In the evaporator 15 and the condenser 12, heat exchange is performed between the cooling water in the cooling-water path 16 and the fluorocarbon in the refrigeration circuit 18. In the cooling-water path 16, a valve 17 is interposed between the evaporator 15 and the condenser 12. In the refrigeration circuit 18, the condenser 12 and the expansion valve 14 have a branch point 18 a therebetween at which the refrigeration circuit 18 is divided into two paths. One path 18 b is in communication with the expansion valve 14 that serves as the decompression means to form a part of refrigeration circuit 18, and the other path 18 c is in communication with an inlet 3 a of the refrigerant passage 3. The path 18 c forms a refrigerant supply path. In the path 18 c, an on-off valve 21 is provided. When the on-off valve 21 is opened, the on-off valve 21 allows the refrigerant to be supplied into the refrigerant passage 3 through the path 18 c. When the on-off valve 21 is closed, the on-off valve 21 prevents the refrigerant from being supplied into the refrigerant passage 3 through the path 18 c. The on-off valve 21 forms refrigerant control means. In the state where the on-off valve 21 is opened, the on-off valve 21 also serves as an expansion valve which is first pressure control means in the refrigerant supply path. The on-off valve 21 is electrically connected to a controller 9 together with the temperature sensor 8. In the controller 9, an upper limit value and a lower limit value about detection value of the temperature sensor 8 are set. The upper limit value serves as a first predetermined temperature and the lower limit value serves as a second predetermined temperature. Also, the expansion valve 14 and the evaporator 15 has a meeting point 18 d therebetween, which is in communication with an outlet 3 b of the refrigerant passage 3 through a path 18 e which forms a refrigerant return path. In the path 18 e, a first accumulator 22 and a constant pressure valve 23 are provided. The accumulator 22 accumulates liquid fluorocarbon therein. The constant pressure valve 23 is second pressure control means in the refrigerant return path for adjusting pressure in the refrigerant passage 3 to a constant value.

Operation of the cooling unit according to the first embodiment will now be described with reference to FIG. 1. When the vacuum treatment unit 1 is started to treat the body 5 in the vacuum chamber 6 of the vacuum treatment unit 1, the compressor 11 is started and at the same time the cooling water circulates through the cooling-water path 16 so that operation of the refrigeration circuit 18 of the chiller unit 10 is started. When the fluorocarbon exchanges heat with the cooling water in the evaporator 15, the fluorocarbon with gas-liquid two-phase flow is evaporated, which is introduced into the compressor 11. The fluorocarbon is compressed by the compressor 11 and is discharged therefrom in the form of gas at high temperature and pressure. When the gaseous fluorocarbon discharged from the compressor 11 exchanges heat with the cooling water cooled by the evaporator 15 in the condenser 12, the gaseous fluorocarbon is cooled thereby to condense the gaseous fluorocarbon into liquid fluorocarbon. Following the condensation of the fluorocarbon in the condenser 12, the liquid fluorocarbon is separated at the branch point 18 a so as to circulate through the paths 18 b, 18 c. As will be described later, when the on-off valve 21 is opened, the fluorocarbon which has circulated through the path 18 c is supplied into the refrigerant passage 3. At this time, the fluorocarbon which has circulated through the path 18 c is decompressed by the on-off valve 21 that serves as the expansion valve, and supplied into the refrigerant passage 3 in the form of gas-liquid two-phase flow. On the other hand, the fluorocarbon which circulates through the path 18 b is decompressed by the expansion valve 14 to form the fluorocarbon with gas-liquid two-phase flow, and then meets the fluorocarbon which has circulated through the path 18 e in the meeting point 18 d as will be described later. Subsequently, when the gas-liquid two-phase flow fluorocarbon flows into the evaporator 15, as described above the gas-liquid two-phase flow fluorocarbon exchanges heat with the cooling water in the cooling-water path 16, thereby to cool the cooling water. Then, the fluorocarbon is returned to the compressor 11, thus circulating through the refrigeration circuit 18.

Now, the fluorocarbon which has been divided into the path 18 c at the branch point 18 a will be described.

In gas-liquid two-phase flow, temperature of the refrigerant is determined in accordance with pressure of the refrigerant. That is, temperature of the gas-liquid two-phase flow fluorocarbon is controlled by adjusting pressure of the fluorocarbon which circulates through the refrigerant passage 3. Therefore, the pressure between the on-off valve 21 and the constant pressure valve 23 is adjusted by the on-off valve 21 and the constant pressure valve 23 so as to meet the temperature of the gas-liquid two-phase flow fluorocarbon.

When the body 5 is treated in the vacuum chamber 6 of the vacuum treatment unit 1, if the detection value of the temperature sensor 8 rises to or above the upper limit value, the controller 9 opens the on-off valve 21 to put the on-off valve 21 into an on mode, thereby allowing the gas-liquid two-phase flow fluorocarbon to flow into the refrigerant passage 3. At this time, the gas-liquid two-phase flow fluorocarbon is passed from the inlet 3 a to the outlet 3 b without drying out in the refrigerant passage 3 at flow rate which enables the fluorocarbon to maintain its gas-liquid two-phase flow from the inlet 3 a to the outlet 3 b. Since the fluorocarbon in the refrigerant passage 3 maintains the gas-liquid two-phase flow, average temperature of a mixture of gas-liquid is maintained at a constant value from the inlet 3 a to the outlet 3 b. The fluorocarbon which has circulated through the outlet 3 b in the form of the gas-liquid two-phase flow is divided into gas and liquid fluorocarbon by the first accumulator 22 located downstream from the outlet 3 b, thereby to prevent liquid fluorocarbon from circulating downstream from the first accumulator 22. Even if the fluorocarbon comes close to drying out in the vicinity of the outlet 3 b, since the liquid fluorocarbon is accumulated in the first accumulator 22, the liquid fluorocarbon accumulated in the accumulator 22 prevents the fluorocarbon in the vicinity of the outlet 3 b from drying out.

When the gas-liquid two-phase flow fluorocarbon circulates through the refrigerant passage 3 to cool the shower plate 2, the detection value of the temperature sensor 8 drops. When the detection value of the temperature sensor 8 drops to or below the lower limit value, the controller 9 closes the on-off valve 21 to put the on-off valve 21 into an off mode, thereby preventing the fluorocarbon from being supplied into the refrigerant passage 3. Thus, the on-off valve 21 is opened and closed in accordance with the detection value of the temperature sensor 8, and as shown in FIG. 2, the on mode in which the refrigerant circulates through the refrigerant passage 3 at flow rate M_(opt) and the off mode in which the refrigerant does not circulate through the refrigerant passage 3 are repeated. That is, on-off control is performed.

The flow rate M_(opt) of the fluorocarbon which circulates through the refrigerant passage 3 will now be described. In order to examine the flow rate M_(opt) of the fluorocarbon which enables the fluorocarbon circulating through the refrigerant passage 3 to maintain the gas-liquid two-phase flow, opening time of the on-off valve 21 per on mode is changed to change the flow rate of the fluorocarbon per on mode thereby to measure temperature fluctuation which is temperature difference between maximum temperature and minimum temperature in the shower plate 2. The result of the measurement is schematically shown in FIG. 3.

When flow rate M of the fluorocarbon is smaller than flow rate M, of the fluorocarbon, temperature difference more than desired temperature difference is caused. This comes from the fact that all the fluorocarbon which circulates through the refrigerant passage 3 dries out in a part of the refrigerant passage 3 adjacent to the outlet 3 b due to the small flow rate M. In other words, this is because all the fluorocarbon is vaporized in the refrigerant passage 3 and absorption of heat from the shower plate 2 utilizing latent heat of vaporization of the fluorocarbon is not performed, resulting in that temperature of the vaporized fluorocarbon rises.

On the other hand, when the flow rate M of the fluorocarbon rises to or above the flow rate M₁, the fluorocarbon maintains a constant rate of absorption of heat without drying out between the inlet 3 a and the outlet 3 b to cool the shower plate 2 thereby to minimize the temperature difference to be Δt₀.

When the flow rate M of the fluorocarbon is larger than flow rate M₂ of the fluorocarbon, the temperature difference is increased in accordance with the increase of the flow rate M. Although in this case the fluorocarbon cools the shower plate 2 without drying out between the inlet 3 a and the outlet 3 b, too large flow rate M cools the shower plate 2 too much than a predetermined temperature per on mode. Consequently, the temperature difference is increased.

Therefore, the flow rate M_(opt) of the fluorocarbon per on mode is so adjusted as to range from the flow rate M₁ to the flow rate M₂ inclusive. The flow rate M_(opt) corresponds to the flow rate of the fluorocarbon which enables the fluorocarbon to maintain the gas-liquid two-phase flow. In addition, the flow rate M_(opt) enables the temperature fluctuation in the shower plate 2 to be minimized. It is noted that the flow rates M₁ and M₂ are not determined by kinds of refrigerants only, but are determined by amount of heat exchange between the shower plate 2 of the vacuum treatment unit 1 and the fluorocarbon. Therefore, the optimal flow rate of the fluorocarbon needs to be determined by conducting the same examination for each object member.

As described above, the on-off valve 21 has the on mode for allowing the condenser 12 to communicate with the refrigerant passage 3, and the off mode for preventing the condenser 12 from communicating with the refrigerant passage 3. When the on-off valve 21 is put into the on mode, the fluorocarbon is rapidly supplied to the refrigerant passage 3 at the flow rate M_(opt), which makes it difficult for the fluorocarbon to dry out in the refrigerant passage 3. When the on-off valve 21 is in the on mode, the fluorocarbon circulates through the refrigerant passage 3 in the form of the gas-liquid two-phase flow, thereby to exchange heat with the shower plate 2 at any position thereof substantially in the same manner during circulation of the fluorocarbon through the refrigerant passage 3. Furthermore, since the on-off valve 21 is switched from the on mode to the off mode, the gas-liquid two-phase flow fluorocarbon does not continuously circulate through the inlet 3 a, which prevents the fluorocarbon from cooling too much only the inlet 3 a.

In the present embodiment, the switch between the on mode and the off mode is performed on the basis of the detection value of the temperature sensor 8, thereby to enable strict temperature control of the shower plate 2.

In the present embodiment, since the cooling unit includes the constant pressure valve 23 that serves as the second pressure control means in addition to the on-off valve 21 that serves as the first pressure control means, pressure control in the refrigerant passage 3 is strictly conducted.

In the evaporator 15, the cooling water in the cooling-water path 16 which cools the condenser 12 is cooled. Therefore, the gas-liquid two-phase flow fluorocarbon with extra cooling capacity is efficiently utilized.

A cooling unit according to a second embodiment of the present invention will now be described with reference to FIG. 4. In the present embodiment, the same reference numerals of FIG. 1 are applied to the same or similar components of FIG. 4, and those descriptions are omitted.

The cooling unit according to the second embodiment differs from that of the first embodiment in that the on-off control is performed by providing a three-way valve at the branch point 18 a of the first embodiment.

In the second embodiment, a chiller unit 30 that serves as cooling means and the refrigerant passage 3 form the cooling unit. The chiller unit 30 has a three-way valve 13 provided at the branch point 18 a of the refrigeration circuit 18 for allowing the condenser 12 to communicate with any one of the refrigerant passage 3 and the expansion valve 14. The three-way valve 13 is electrically connected to the controller 9 together with the temperature sensor 8. It is noted that the three-way valve 13 forms the refrigerant control means and the first pressure control means provided in the refrigerant supply path. That is, the three-way valve 13 controls the circulation of the refrigerant into the path 18 c to decompress the refrigerant in the path 18 c. The other structure of the second embodiment is substantially the same as that of the first embodiment.

In the second embodiment, when the shower plate 2 does not need to be cooled, the controller 9 sets the direction of the three-way valve 13 so as to allow the condenser 12 to communicate with the expansion valve 14. When the body 5 is treated in the vacuum chamber 6 of the vacuum treatment unit 1, if the detection value of the temperature sensor 8 rises to or above the upper limit value, the controller 9 switches the direction of the three-way valve 13 so as to allow the condenser 12 to communicate with the refrigerant passage 3, thereby supplying the refrigerant passage 3 with the fluorocarbon. At this time, the fluorocarbon is supplied into the refrigerant passage 3 at flow rate which enables the fluorocarbon to maintain its gas-liquid two-phase flow from the inlet 3 a to the outlet 3 b as is the case with the first embodiment. If the shower plate 2 is cooled so that the detection value of the temperature sensor 8 drops to or below the lower limit value, the controller 9 switches the direction of the three-way valve 13 so as to allow the condenser 12 to communicate with the expansion valve 14 again. The other operation is substantially the same as that of the first embodiment.

As described above, the on-off control is performed by switching the direction of the three-way valve 13 on the basis of the detection value of the temperature sensor 8. Therefore, the same effects as those of the first embodiment are substantially obtained.

A cooling unit according to a third embodiment of the present invention will now be described with reference to FIG. 5. In the present embodiment, the same reference numerals of FIG. 1 are applied to the same or similar components of FIG. 5, and those descriptions are omitted. The cooling unit according to the third embodiment differs from that of the first embodiment in that gas-liquid separator is provided in the path 18 c of the first embodiment.

In the present embodiment, a chiller unit 50 that serves as cooling means and the refrigerant passage 3 form the cooling unit. The chiller unit 50 includes a receiver 41 that serves as gas-liquid separation means which is provided between the on-off valve 21 and the branch point 18 a. The receiver 41 has a tank 41 a in which the fluorocarbon with the gas-liquid two-phase flow is accumulated, a gas phase pipe 41 b which communicates with gas phase in the tank 41 a, and a liquid phase pipe 41 c which communicates with liquid phase in the tank 41 a. The gas phase pipe 41 b is connected to one end of a path 18 c 1 the other end of which is the branch point 18 a. On the other hand, the liquid phase pipe 41 c is connected to one end of a path 18 c 2 the other end of which is connected to the inlet 3 a of the refrigerant passage 3. The paths 18 c 1 and 18 c 2 form the refrigerant supply path. The other structure of the third embodiment is substantially the same as that of the first embodiment.

In the present embodiment, when the on-off valve 21 is opened, at least a part of the fluorocarbon which circulates through the refrigeration circuit 18 is circulated from the branch point 18 a into the path 18 c 1. The fluorocarbon which circulates through the path 18 c 1 is released from the gas phase pipe 41 a of the receiver 41 into the gas phase in the tank 41 a.

In the refrigeration circuit 18, when the fluorocarbon in the condenser 12 is not completely condensed into liquid fluorocarbon due to insufficient cooling, gas component such as vaporized fluorocarbon or air gets mixed with the liquid fluorocarbon at the branch point 18 a. When such liquid fluorocarbon containing the gas component is released into the tank 41 a, the liquid fluorocarbon is separated from the gas component. The fluorocarbon which is supplied into the path 18 c 2 through the liquid phase pipe 41 c is liquid fluorocarbon which does not contain the gas component. When such liquid fluorocarbon which does not contain the gas component circulates through the refrigerant passage 3 in the form of the gas-liquid two-phase flow, the fluorocarbon is not influenced by the contained gas component. Therefore, the fluorocarbon is circulated through the refrigerant passage 3 at a completely constant temperature thereby to prevent degradation of the cooling efficiency. Thus, the temperature of the shower plate 2 is still more strictly controlled. The other operation is substantially the same as that of the first embodiment, and therefore, the same effects as those of the first embodiment are substantially obtained.

A cooling unit according to a fourth embodiment of the present invention will now be described with reference to FIG. 6. In the present embodiment, the same reference numerals of FIG. 1 are applied to the same or similar components of FIG. 6, and those descriptions are omitted. The cooling unit according to the fourth embodiment differs from that of the first embodiment in that the meeting point 18 d of the first embodiment between the path 18 e and the refrigeration circuit 18 is located between the evaporator 15 and the compressor 11.

In the fourth embodiment, a chiller unit 70 that serves as cooling means and the refrigerant passage 3 form the cooling unit. In the chiller unit 70, the meeting point 18 d between the path 18 e and the refrigeration circuit 18 is located between the evaporator 15 and the compressor 11. The chiller unit 70 includes a second accumulator 24 provided between the meeting point 18 d and the compressor 11 for preventing the liquid fluorocarbon from flowing into the compressor 11. The other structure of the fourth embodiment is substantially the same as that of the first embodiment.

The fluorocarbon which has cooled the shower plate 2 as is the case with the first embodiment is controlled by the on-off valve 21 to maintain its gas-liquid two-phase flow between the inlet 3 a and the outlet 3 b. After the fluorocarbon has passed through the first accumulator 22, the fluorocarbon is normally vaporized and is mixed with the fluorocarbon which circulates through the refrigeration circuit 18 at the meeting point 18 d to be drawn into the compressor 11. When the flow rate of the fluorocarbon which circulates through the path 18 e is too large or when the temperature of the chiller unit 70 is relatively low, however, there is a possibility that the liquid fluorocarbon flows from the first accumulator 22 downstream. If the liquid fluorocarbon is drawn into the compressor 11 still after the liquid fluorocarbon is mixed with the fluorocarbon which circulates through the refrigeration circuit 18 at the meeting point 18 d, there is fear that the compressor 11 does not work. For this reason, the liquid fluorocarbon is accumulated in the second accumulator 24 to completely vaporize the fluorocarbon downstream of the second accumulator 24, thereby to protect the compressor 11. The other operation is substantially the same as that of the first embodiment, and therefore, the same effects as those of the first embodiment are substantially obtained.

Although in the fourth embodiment the meeting point 18 d of the first embodiment between the path 18 e and the refrigeration circuit 18 is located between the evaporator 15 and the compressor 11, the location of each meeting point 18 d of cooling units according to the second and third embodiments may be applied to the fourth embodiment. In this case, the second accumulator 24 is disposed between the evaporator 15 and the compressor 11.

A cooling unit according to a fifth embodiment of the present invention will now be described. The cooling unit according to the fifth embodiment differs from that of the first embodiment in that a duty ratio which represents a ratio of on mode time to total time of the on mode time and off mode time is adjusted on the basis of the detection value of the temperature sensor 8 thereby to control the circulation of the fluorocarbon in the refrigerant passage 3. In the present specification, the on mode time means an on mode period of time and the off mode time means an off mode period of time. The structure of the cooling unit according to the fifth embodiment is substantially the same as that according to the first embodiment.

As shown in FIG. 1, as is the case with the first embodiment, the body 5 is treated in the vacuum chamber 6 of the vacuum treatment unit 1. During the treatment of the body 5, the controller 9 opens and closes the on-off valve 21 so as to alternately put the on-off valve 21 into the on mode in which the fluorocarbon circulate at the flow rate M_(opt) and the off mode in which the fluorocarbon does not circulate as shown in FIG. 7, thereby to circulate the fluorocarbon into the refrigerant passage 3. It is noted that the total time of the on mode time and the off mode time subsequent to the on mode time is constantly set as a constant time ΔT. For example, when the circulation of the fluorocarbon in the refrigerant passage 3 is controlled at a duty ratio R₀, and the on-mode time is Δt₁ and the off mode time is Δt₂, the duty ratio R₀ is represented by Δt₁/(Δt₁+Δt₂) where ΔT=Δt₁+Δt₂. While the circulation of the fluorocarbon in the refrigerant passage 3 is controlled at the duty ratio R₀, if the detection value of the temperature sensor 8 rises above the upper limit value that serves as the first predetermined temperature, the controller 9 raises the duty ratio R₀ to R₁ (>R₀) on the basis of the temperature difference between the detection value of the temperature sensor 8 and the upper limit value. The controller 9 opens and closes the on-off valve 21 in accordance with the duty ratio R₁ thereby to allow the refrigerant passage 3 to communicate with the condenser 12 or to prevent the refrigerant passage 3 from communicating with the condenser 12. Thus, cooling capacity for the shower plate 2 is raised thereby to lower the temperature of the shower plate 2. Then, while the circulation of the fluorocarbon in the refrigerant passage 3 is controlled at the duty ratio R₁, if the detection value of the temperature sensor 8 drops below the lower limit value that serves as the second predetermined temperature, the controller 9 lowers the duty ratio R₁ to R₂ (<R₀) on the basis of the temperature difference between the detection value of the temperature sensor 8 and the lower limit value. The controller 9 opens and closes the on-off valve 21 in accordance with the duty ratio R₂ thereby to allow the refrigerant passage 3 to communicate with the condenser 12 or to prevent the refrigerant passage 3 from communicating with the condenser 12. Thus, cooling capacity for the shower plate 2 is lowered and therefore the temperature of the shower plate 2 rises. The other operation is substantially the same as that of the first embodiment.

It is noted that the controller 9 has a map for representing an increase or decrease of the duty ratio in accordance with the temperature difference between the detection value of the temperature sensor 8 and the upper limit value or the lower limit value to change the duty ratio.

As described above, the controller 9 changes the duty ratio on the basis of the detection value of the temperature sensor 8 to open and close the on-off valve 21 in accordance with the duty ratio, thereby to allow the refrigerant passage 3 to communicate with the condenser 12 or to prevent the refrigerant passage 3 from communicating with the condenser 12. Thus, the controller 9 controls the circulation of the fluorocarbon in the refrigerant passage 3. Consequently, cooling capacity for the shower plate 2 is sensitively controlled. In addition, since the cooling capacity is sensitively controlled, dispersion of the temperature of the shower plate 2 is reduced.

The fifth embodiment is modified from the first embodiment so that the duty ratio of the first embodiment is changed on the basis of the detection value of the temperature sensor 8 to control the on-off valve 21 in accordance with the duty ratio, thereby to allow the refrigerant passage 3 to communicate with the condenser 12 or to prevent the refrigerant passage 3 from communicating with the condenser 12, which controls the circulation of the fluorocarbon in the refrigerant passage 3. However, the fifth embodiment is not limited to the above modification to the first embodiment. The fifth embodiment may be modified from the second through fourth embodiments so that the three-way valve 13 or the on-of valve 21 is controlled in accordance with the duty ratio.

Although in the first through fifth embodiments fluorocarbon is used as a refrigerant, the refrigerant is not limited to fluorocarbon. Hydrocarbon such as propane or isobutane may be used. Mixed refrigerant besides fluorocarbon and hydrocarbon may also be used. For example, mixed refrigerant 407C may be used as a mixed refrigerant.

Although in the first through fifth embodiments these cooling units are used for the semiconductor production unit, the cooling units are not limited to the above use. Each cooling unit can be used as a unit for cooling every object member of cooling, in particular, as a cooling unit which requires strict temperature control.

Although in the first through fifth embodiments a diaphragm type compressor 11 is used as a compressor, the compressor is not limited to this type. For example, when the compressor is used for the cooling unit used for the semiconductor production unit, a diaphragm type oil free compressor in which oil is not mixed with the refrigerant is preferable. When the compressor is used for the cooling unit for cooling the other object member of cooling, the compressor is not limited to the oil free compressor but a known piston type compressor or a scroll type compressor may be used.

Although in the first through fifth embodiments both a switch from the on mode to the off mode and a switch from the off mode to the on mode are performed on the basis of the detection value of the temperature sensor 8, both of the switches are not limited to the above performance. The on-off valve 21 may be formed so as to be put into the on mode time for a predetermined time and then be automatically switched from the on mode time to the off mode after the predetermined time.

In this case, the on-off valve 21 is reliably switched from the on mode time to the off mode in the predetermined time. Compared to the case where the on-off valve 21 is switched from the on mode time to the off mode on the basis of the detection value of the temperature sensor 8, delay of the control caused by delay of reaction of the temperature sensor 8, what is called, overshoot is prevented.

Although in the second embodiment the expansion valve 14 is disposed in the refrigeration circuit 18, the three-way valve 13 may be provided with decompression functions of the expansion valve 14. In this case, the fluorocarbon which circulates through the evaporator 15 is decompressed by the three-way valve 13. This enables the cooling unit to reduce the number of parts, which prevents the refrigeration circuit from being complicated.

Although in the first through fifth embodiments the constant pressure valve 23 is disposed in the path 18 e, pressure in the refrigerant passage 3 may be controlled by only the on-off valve 21 and the three-way valve 13 without the constant pressure valve 23.

Although illustrative embodiments of the present invention, and various modifications thereof, have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and the described modifications, and that various changes and further modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. 

1. A cooling unit containing refrigerant for exchanging heat with an object member of cooling, the cooling unit comprising: a refrigerant passage which allows the refrigerant to circulate therethrough; cooling means communicating with the refrigerant passage for supplying the refrigerant passage with the refrigerant, the cooling means comprising: a refrigeration circuit which allows the refrigerant to circulate therethrough; a compressor disposed in the refrigeration circuit; a condenser also disposed in the refrigeration circuit; decompression means also disposed in the refrigeration circuit; an evaporator also disposed in the refrigeration circuit; a refrigerant supply path one end of which is connected to a part of the refrigeration circuit between the condenser and the decompression means and the other end of which is connected to an inlet of the refrigerant passage; a refrigerant return path one end of which is connected to an outlet of the refrigerant passage and the other end of which is located downstream from the decompression means and is connected to a part of the refrigeration circuit between the decompression means and the compressor; refrigerant control means disposed in the refrigerant supply path for allowing the condenser to communicate with the refrigerant passage or preventing the condenser from communicating with the refrigerant passage; and first pressure control means also disposed in the refrigerant supply path for controlling pressure in the refrigerant passage, wherein the refrigerant control means has an on mode which allows the refrigerant to circulate through the refrigerant passage at a flow rate which enables the refrigerant to maintain gas-liquid two-phase flow by allowing the condenser to communicate with the refrigerant passage, and an off mode which prevents the refrigerant from circulating through the refrigerant passage by preventing the condenser from communicating with the refrigerant passage.
 2. The cooling unit according to claim 1, further comprising temperature detection means for detecting temperature of the object member or vicinity of the object member, wherein when detection value detected by the temperature detection means rises to or above a first predetermined temperature, the refrigerant control means is put into the on mode, and wherein when the detection value detected by the temperature detection means drops to or below a second predetermined temperature which is lower than the first predetermined temperature, the refrigerant control means is put into the off mode.
 3. The cooling unit according to claim 1, further comprising temperature detection means for detecting temperature of the object member or vicinity of the object member, wherein when detection value detected by the temperature detection means rises to or above a first predetermined temperature, the refrigerant control means is put into the on mode for a predetermined time.
 4. The cooling unit according to claim 1, further comprising temperature detection means for detecting temperature of the object member or vicinity of the object member, wherein the refrigerant control means sets a duty ratio which represents a ratio of on mode time to total time of the on mode time and off mode time with the total time kept at a constant time and at the same time changes the duty ratio on the basis of detection value detected by the temperature detection means thereby to allow the condenser to communicate with the refrigerant passage or to prevent the condenser from communicating with the refrigerant passage in accordance with the duty ratio.
 5. The cooling unit according to claim 4, wherein when the detection value detected by the temperature detection means rises to or above a first predetermined temperature, the refrigerant control means raises the duty ratio on the basis of difference between the detection value and the first predetermined temperature, and when the detection value detected by the temperature detection means drops to or below a second predetermined temperature which is lower than the first predetermined temperature, the refrigerant control means lowers the duty ratio on the basis of difference between the detection value and the second predetermined temperature.
 6. The cooling unit according to claim 1, wherein the refrigerant control means is an on-off valve for allowing the refrigerant to circulate through the refrigerant supply path or preventing the refrigerant from circulating through the refrigerant supply path.
 7. The cooling unit according to claim 1, wherein the refrigerant control means is a three-way valve for allowing the condenser to communicate with any one of the refrigerant passage and the decompression means.
 8. The cooling unit according to claim 1, further comprising gas-liquid separation means upstream from the refrigerant control means in the refrigerant supply path for separating the refrigerant into liquid refrigerant and gas refrigerant.
 9. The cooling unit according to claim 1, further comprising second pressure control means disposed in the refrigerant return path, wherein a first accumulator is disposed upstream from the second pressure control means in the refrigerant return path.
 10. The cooling unit according to claim 9, wherein the other end of the refrigerant return path is connected to a part of the refrigeration circuit between the decompression means and the evaporator.
 11. The cooling unit according to claim 9, wherein the other end of the refrigerant return path is connected to a part of the refrigeration circuit between the evaporator and the compressor, and wherein a second accumulator is disposed in a part of the refrigerant return path and the refrigeration circuit between the second pressure control means and the compressor.
 12. The cooling unit according to claim 1, further containing cooling water for exchanging heat with the refrigerant in the condenser, wherein the cooling water exchanges heat with the refrigerant in the evaporator.
 13. The cooling unit according to claim 1, wherein the first pressure control means also serves as the refrigerant control means.
 14. The cooling unit according to claim 1, further comprising a constant pressure valve disposed in the refrigerant return path for controlling pressure in the refrigerant passage. 